Conventionally, for non-aqueous electrolyte secondary batteries, typically, a non-aqueous electrolyte solution is used which has, for example, a lithium salt such as lithium hexafluorophosphate dissolved as an electrolyte salt in a non-aqueous solvent such as ethylene carbonate or dimethyl carbonate, a lithium-transition metal composite oxide is used as a positive electrode active material, and a carbon material is used as a negative electrode active material. In addition, the use of two or more non-aqueous solvents in the form of a mixture has been proposed in these non-aqueous electrolyte secondary batteries.
For example, Japanese Patent Application Laid-Open No. 2009-206072 (hereinafter, referred to as Patent Document 1) proposes a solvent for dissolving an electrolyte salt in a lithium secondary battery, which contains at least one fluorine-based solvent selected from the group consisting of fluorine-containing ether, fluorine-containing ester, and fluorine-containing chain carbonate, and contains 1,2-dialkyl-1,2-difluoroethylenecarbonate. In addition, Patent Document 1 discloses the action of providing flame-retardant electrolyte solutions, and further effects such as improvements in battery rate characteristics, which are achieved by the use of the solvent mentioned above.
Patent Document 1: Japanese Patent Application Laid-Open No. 2009-206072